I installed Gentoo succesfully.
Would it be of any benefit to remerge the same version of gcc (compile it from scratch)?
Would there be some kind of speed improvement if I recompile it with the optimized settings for my cpu?

Too little information. If you just installed Gentoo and haven't done emerge -e world yet (with your CFLAGS) I'd do it. Or you could wait until package upgrades will take care of it for you._________________Please learn how to denote units correctly!

You might also consider that the marginal increase in performances this will provide is not worth rebuilding everything 2 times, 3 times and... even more, immediately.
If you stuck to stable arch for gcc, be aware that gcc-4.6 should go stable in a very near furture.
So, you might find wise to postpone all this work until then._________________

because gcc is father of tools, don't you think building it 2-3 times to make sure you will end with the tool that is use to produce binary actually work and produce valid binary. Not all distros have slots features to saved you from a dead gcc. The highest optimization can produce valid code that will produce invalid/unexpected results.

rebulding a gcc always have positive effect (stability or speed) when upgrading glibc, glibc (or you current libc version) is tied with gcc as gcc hack their header to add fix, optimizations or arch specific things. Just browse the forum to see how many users get lost by weird problem appears in their programs as they use a bork toolchain, generally after upgrading glibc.
As you have install gentoo, it's more than certain your glibc were update too in the process.

4.4.7 is the only version I can use.
Packages are failing with the latest stable 4.5.* and the latest unstable 4.6.* series.
I will see if the lack of "env-update" solves the problem.
Thanks for the tip to the GCC guide.
I always follow the guide to the letter (kind of lol)
it just looks like I missed out the env-update part._________________Whatever you do, do it properly!